by Laura Cuppini
Study on fruit flies demonstrates the role of a steroid hormone, ecdysone, similar to estrogen and testosterone
Man, like animals, is born and grows until, at a specific moment in life, physical development stops. In humans this phase coincides with puberty, but the exact mechanisms that cause growth to stop are not known. A study from the University of Illinois at Chicago, pubblicato su Proceedings of the National Academy of Sciences (Pnas), investigated the phenomenon by observing fruit flies (Drosophila melanogaster), widely used in scientific research. In these insects, puberty occurs during the transition from larvae to adults.
The critical weight
According to a theory widely shared by the scientific community, a larva stops growing when it reaches a certain body size. The authors of the new study instead wanted to demonstrate a particular hypothesis that brings into play the interactions between body size, production of ecdysone (a steroid hormone) and nutritional information, suggesting that the phenomenon of the so-called critical weight, observed in Drosophila larvae, not a direct consequence of a size-sensing mechanism, but rather an indirect consequence of the physiological mechanisms regulating growth and ecdysone synthesis. In particular, reaching critical weight would reflect a change in ecdysone regulation, i.e. a shift from external factors (insulin/insulin-like growth factor signaling and prothoracicotropic hormone) to internal factors (ecdysone itself and ecdysone receptor).
Mathematical model
The “decision” to interrupt growth and enter adulthood is a critical point in development that determines body size, with an impact on multiple aspects of biology – write the authors of the study -. In many animals, stunting is a consequence of the release of hormones and appears to be linked to the achievement of a particular body size or condition. However, the size-sensing mechanism used by animals to initiate hormone synthesis is poorly understood. We have developed a simple mathematical model to “measure” growth arrest in Drosophila melanogaster. The achievement of the “critical weight” was related to the synthesis of ecdysone. Our model suggests that the size-sensing mechanism that initiates metamorphosis occurs before the larva reaches “critical weight.” This mechanism is linked to the interactions between body size, ecdysone and nutritional “information”. Because many aspects are evolutionarily conserved, the model can provide a general framework for understanding how animals transition from juvenile to adult form.
Steroid hormone
The authors of the study therefore hypothesized that in the fruit fly the growth interruption has to do with ecdysone, which is similar to estrogen (the main female sex hormones) and testosterone (male sex hormone). The researchers used a mathematical model to demonstrate that body size is not the trigger for stunting in the fruit fly. The growth stop switch activated by the gland that produces ecdysone. In the larval stage, the gland receives nutritional information useful for regulating ecdysone production. But at a certain point the gland no longer needs external input to make decisions. The increase in ecdysone titer determines growth arrest, fixing the final size of the body and pushes metamorphosis into the adult form, the researchers write.
Early puberty
According to Alexander Shingleton, a biologist at the University of Illinois who led the study, the mechanism that occurs in the fruit fly could be similar to that which occurs in humans, given that similar steroid hormones are involved. Additionally, both fruit flies and humans transmit nutritional information via insulin. In humans the stop signal occurs around puberty, although it takes several years before growth actually stops. We know that today, in boys, the onset of puberty tends to appear earlier and earlier: to understand this phenomenon we need to know the underlying mechanism, concluded Shingleton.
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December 12, 2023 (changed December 12, 2023 | 08:00)
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